Here are the resulting rendering done with default value with 2.6 engine ( be sure that you are really using default value in rendering, meaning, antighost preset should be selected if not not selected ).

First screenshot is about direct detection without color correction. It highlights the fact that some images don't have the same exposure as the rest of the panorama ( explained in next post ).Second screenshot is color corrected panorama. I used gamma/exposure/color anchors over the whole image with the same default color anchor reference.3rd screenshot : Rendering done with default value ( antighost preset ) on panorama without and with color correction.You can notice that even without color correction the blending is done on a large area around dark images. If you used 0 as multiband level, it can even be larger.With color correction, you don't have any issue in blending.4rd screenshot. I tried to find issue in blending by using a fairly aggressive level on the image ( dark point is the darkest point of the sky, white point is the brightest point of the sky ). You can see that even with this huge level alteration, the blending in smooth along all sky.

About exposure difference. We used a modified dcraw converter, the same that is embedded into xnview in fact.Or it seems that there is an issue in this part. See the following 2 screenshots. First is previewing these raw with xnview ( notice the exposure shift ) and second is previewing the raw with Camera Raw ( no exposure shift ). We need to find this issue on raw decoding.